.loader {
    border: 16px solid #f3f3f3;
    border-top: 16px solid #3498db;
    border-radius: 50%;
    width: 120px;
    height: 120px;
    animation: spin 2s linear infinite;
    margin: auto;
    display: none; /* 初始隐藏 */
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}